1. Field of the Invention
The present invention relates generally to level sensors for liquid storage tanks. This invention more particularly relates to level sensors and operational circuitry therefor.
2. Background Information
Level sensors (e.g., float sensors) are commonly used to indicate the liquid level in a liquid storage vessel. For example, liquid storage tanks for fuel, oil, propane, natural gas, and anhydrous ammonia typically include one or more level sensors for indicating the liquid level therein. A typical level sensor includes a float arm, which translates the vertical displacement caused by changes in the liquid level to rotation of a drive magnet. A dial indicator disposed externally of the tank includes a mating pointer/magnet assembly that is typically coupled by magnetic flux to the drive magnet. As the drive magnet turns, the pointer magnet similarly rotates, and a pointer typically gives a visual indication of tank level. In addition there are numerous commercial devices that not only offer visual indication of level, but may also provide an electric signal proportional to level. For example the Hall Effect Twin Site Sender(trademark) manufactured by Rochester Gauges, Inc., Dallas, Tex. utilizes a Hall effect sensor and provides a voltage output proportional to level. A similar device is also disclosed in U.S. Pat. No. 4,554,494 to Howeth. Alternatively, the Advanced Matrix Film Twin Site Sender(trademark) also manufactured by Rochester Gauges, Inc., Dallas Tex., includes a pointer with a wiper assembly coupled to a conductive substrate forming a potentiometer whose output is proportional to level. A similar device is also disclosed in U.S. Pat. No. 5,357,815 to Williamson.
For many applications, such as industrial storage of liquid propane, oil, liquefied natural gas, ammonia, and other liquids, in which large numbers of tanks are employed, remote indication may be desirable. Robertshaw Control Company, Inc., of Richmond, Va. (the assignee of the present application) currently markets the Centeron(copyright) level monitoring system for the purpose of remotely monitoring the liquid level in liquid storage vessels. In some applications a single tank may include two or more level sensors (e.g., owing to the aspect ratio of the tank as discussed in more detail hereinbelow). Additionally, in the same or other applications, two or more tanks may be coupled together (e.g., through a manifold). Remote determination of the liquid level in these applications is more challenging, and therefore, there exists a need for an improved level sensor, and in particular, improved operational circuitry therefore.
One aspect of the present invention includes a material level measuring apparatus including a plurality of level sensor input ports each configured to receive an electrical signal corresponding to a material level in a storage vessel portion. An input circuit is configured to combine the received electrical signals and to generate an output signal that corresponds to a combined material level in a plurality of the storage vessel portions.
In another aspect, a liquid level measuring apparatus includes a plurality of level sensors each configured to generate an electrical signal proportional to a liquid level in a liquid storage vessel portion. An input circuit is provided, which has a plurality of input ports couplable to the plurality of level sensors. The input circuit is configured to receive the electrical signal from each of the plurality of level sensors, and includes an averaging circuit configured to combine the electrical signals. The averaging circuit has a plurality of resistors connected in parallel and at least one switch connected in series with at least one of the plurality of resistors, the switch being configured to selectively open and close a portion of the averaging circuit. The input circuit also includes a plurality of voltage followers, a single one of the voltage followers being connected in series with each of the plurality of resistors. The input circuit is configured to generate a single output signal which is proportional to the combined liquid level in a plurality of liquid storage vessel portions.
Another aspect of the invention includes an input circuit for a liquid level monitoring device. The input circuit includes a plurality of level sensor input ports each configured to receive an electrical signal corresponding to a material level in a storage vessel portion. The input circuit also includes a plurality of resistors connected in parallel and at least one switch connected in series with at least one of the resistors. The switch is configured to selectively open and close a portion of the input circuit. A plurality of voltage followers are respectively coupled in series with each of the resistors. The input circuit is configured to generate an output signal corresponding to a combined material level in a plurality of the storage vessel portions.
A still further aspect of the present invention includes a method for fabricating a liquid level measuring apparatus, including configuring a plurality of level sensor input ports to receive an electrical signal corresponding to a material level in a storage vessel portion. The method further includes coupling the input ports to an input circuit, configuring the input circuit to combine the received electrical signals; and configuring the input circuit to generate an output signal corresponding to a combined material level in a plurality of the storage vessel portions.